Haowen Liang

In flat lenses, focusing typically arises from the interference of first-order diffracted light after the incident optical field passes through the lens structure. However, the focused field exhibits a fundamental trade-off between achieving a narrow lateral focal width and maintaining an extended longitudinal focal depth. This limitation poses a significant challenge for simultaneously realizing high lateral resolution and large imaging depth in practical imaging systems. To overcome this constraint, we propose a multi-level diffractive lens (MDL) architecture in which focusing is produced by the constructive interference of multiple diffraction orders. Based on this principle, broadband light in the wavelength range of 800–900 nm is focused into an optical needle with an average lateral focal width of 2.4 μm and a longitudinal focal depth of 2640 μm, corresponding to an exceptional depth-to-width ratio of 1100:1. The fabricated MDL is integrated into a spectral-domain optical coherence tomography (SD-OCT) system, yielding nearly a 9-fold improvement in imaging depth compared with conventional objective lens-based OCT systems over comparable lateral resolution. These results demonstrate the strong potential of the proposed MDL for high-resolution imaging applications such as clinical diagnostics and defect inspection.

The advancement of high-resolution optical imaging places increasing demand on compact objective lenses. A key challenge is to achieve both a wide field of view (FOV) and high imaging resolution. A metalens doublet addresses this by using one layer to correct aberrations and another to focus, with combined phase profiles analytically designed for diffraction-limited performance. Here, we demonstrate a polarization-insensitive metalens doublet at 808 nm. Its imaging performance is experimentally validated using a 1951 USAF resolution chart, clearly resolving Group 10, Element 3, corresponding to a half-pitch resolution of 388 nm. Notably, this resolution is maintained across the entire 12° FOV, which corresponds to a circular imaging area with a diameter of 40.0 μm. These results show that the proposed metalens doublet enables uniform high-resolution imaging over a wide field in a compact platform, highlighting its potential for miniaturized microscopes and other compact optical imaging systems.

Augmented reality (AR) has garnered significant attention in recent years for its advanced display capabilities. High-performing AR demands lightweight and integrated optical components. Metalenses offer a solution, as they can meet these requirements through their multifunctional and integrative potential. In this work, we propose a trans-reflective red–green–blue (RGB) achromatic AR metalens composed of titanium dioxide (TiO₂) nanopillars and a multiwavelength notch filter. The AR metalens achieves balanced focusing efficiencies for obliquely incident light, with a field of view exceeding 90°, which ensures excellent readability in various scenarios for AR devices. Additionally, ambient light can pass efficiently through the metalens. This design functions both as an eyepiece and an optical combiner, demonstrating strong potential for AR applications. © 2026 Chinese Optics Letters

Strongly scattering conditions are detrimental to imaging. Conventional methods rely solely on post-processing techniques to enhance the ballistic components of an obscured target to recover the image; however, they struggle in complex conditions where the ballistic components are heavily overwhelmed by scattering. In this work, we present an optical meta-image-processor (MIP) that tailors the scattered point spread function of the imaging system to enable high-quality, deep imaging through strongly scattering media. The MIP performs both Laplacian and Gaussian operations in a single device, effectively suppressing background interference and Gaussian noise in the obscured image. Experimental results demonstrate that clear information can be recognized with the MIP, even when the optical thickness of the scattering medium reaches a challenging value of 17.05. Without the MIP, such imaging depth cannot be achieved through direct imaging, even when combined with any other post-processing techniques. Additionally, the MIP shows potential for enhancing the diagnostic performance of fundus cameras in the presence of cataracts. Both simulated and experimental evidence confirms the MIP’s capability to reveal hidden information under strongly scattering conditions, underscoring its promising potential to enhance imaging depth in biomedical imaging, machine vision, and artificial intelligence, especially in complex environments.

Optical metasurfaces enable compact, lightweight and planar optical devices. Their performances, however, are still limited by design approximations imposed by their macroscopic dimensions. To address this problem, we propose a neural network-based multi-stage gradient optimization method to efficiently modulate nonlocal interactions between meta-atoms, which is one of the major effects neglected by current design methods. Our strategy allows for the use of these interactions as an additional design dimension to enhance the performance of metasurfaces and can be used to optimize large-scale metasurfaces with multiple parameters. As an example of application, we design a meta-hologram with a zero-order energy suppressed to 26% (theoretically) and 57% (experimentally) of its original value. Our results suggest that neural networks can be used as a powerful design tool for the next generation of high-performance metasurfaces with complex functionalities.

High‐resolution metalens with high numerical aperture (NA) and large areas are essential for advancing integrated display technologies. However, chromatic aberrations impose significant limitations on their practical applications. Although multi‐wavelength achromatic designs mitigate this issue, challenges such as low imaging resolution and degraded imaging quality persist. In this study, an RGB achromatic metalens is demonstrated with an experimentally achieved diameter of 410 µm, achieving a high imaging resolution of 0.775 µm in digital imaging systems. To address imaging blurriness caused by spatial multiplexing, it further integrates neural network‐based image restoration, leading to significant improvements in imaging performance. This work highlights the potential of the high‐resolution RGB achromatic metalens for diverse digital imaging applications, including digital projectors, virtual reality headsets, and augmented reality glasses.

Flat optics have attracted interest for decades due to their flexibility in manipulating optical wave properties, which allows the miniaturization of bulky optical assemblies into integrated planar components. Recent advances in achromatic flat lenses have shown promising applications in various fields. However, it is a significant challenge for achromatic flat lenses with a high numerical aperture to simultaneously achieve broad bandwidth and expand the aperture sizes. Here, we present the zone division multiplex of the meta-atoms on a stepwise phase dispersion compensation (SPDC) layer to address the above challenge. In principle, the aperture size can be freely enlarged by increasing the optical thickness difference between the central and marginal zones of the SPDC layer, without the limit of the achromatic bandwidth. The SPDC layer also serves as the substrate, making the device thinner. Two achromatic flat lenses of 500 nm thickness with a bandwidth of 650–1000 nm are experimentally achieved: one with a numerical aperture of 0.9 and a radius of 20.1 µm, and another with a numerical aperture of 0.7 and a radius of 30.0 µm. To the best of our knowledge, they are the broadband achromatic flat lenses with highest numerical apertures, the largest aperture sizes and thinnest thickness reported so far. Microscopic imaging with a 1.10 µm resolution has also been demonstrated by white light illumination, surpassing any previously reported resolution attained by achromatic metalenses and multi-level diffractive lenses. These unprecedented performances mark a substantial step toward practical applications of flat lenses.

Efficient design methods for large-scale metalenses are crucial for various applications. The conventional phase-mapping method shows a weak performance under large phase gradients, thus limiting the efficiency and quality of large-scale, high-numerical-aperture metalenses. While inverse design methods can partially address this issue, existing solutions either accommodate only small-scale metalenses due to high computational demands or compromise on focusing performance. We propose an efficient large-scale design method based on an optimization approach combined with the adjoint-based method and the level-set method, which first forms a one-dimensional metalens and then extends it to two dimensions. Taking fabrication constraints into account, our optimization method for large-area metalenses with a near-unity numerical aperture (NA = 0.99) has improved the focusing efficiency from 42% to 60% in simulations compared to the conventional design method. Additionally, it has reduced the deformation of the focusing spot caused by the ultrahigh numerical aperture. This approach retains the benefits of the adjoint-based method while significantly reducing the computational burden, thereby advancing the development of large-scale metalenses design. It can also be extended to other large-scale metasurface designs.

The resolution of an optical microscope is determined by the overall point spread function of the system. When examining structures significantly smaller than the wavelength of light, the contribution of the background or surrounding environment can profoundly affect the point spread function. This research delves into the impact of reflective planar substrate structures on the system’s resolution. We establish a comprehensive forward imaging model for a reflection-type confocal laser scanning optical microscope, incorporating vector field manipulation to image densely packed nanoparticle clusters. Both theoretical and experimental findings indicate that the substrate causes an interference effect between the background field and the scattered field from the nanoparticles, markedly enhancing the overall spatial resolution. The integration of vector field manipulation with an interferometric scattering approach results in superior spatial resolution for imaging isolated particles and densely distributed nanoscale particle clusters even with deep subwavelength gaps as small as 20 nm between them. However, the method still struggles to resolve nanoparticles positioned directly next to each other without any gap, necessitating further work to enhance the resolving ability. This may involve techniques like deconvolution or machine learning-based post-processing methods.